The present invention relates to an adjustable vehicle roof having a folding top, and more particularly, to a roof whose folding top can be adjusted between a closed position and a deposited position with a folding top linkage and a folding top covering material, with a material holding bow which is assigned to the folding top linkage and which, in the closed position of the folding top, rests on a rearward, vehicle-body-side component and applies tension to the folding top covering material, with a tensioning hoop which acts upon the material holding bow in the closed position and which is supported on the folding top linkage and has an articulation arrangement with at least one hinge axis transversely arranged with respect to the longitudinal axis of the vehicle, the articulation arrangement being constructed as over-dead-center kinematics.
DE 41 23 516 C1 describes a folding top comprising a plurality of roof frames, bows and hoops assigned to the folding top linkage. The folding top linkage is adjustable by adjusting kinematics between a closed position covering the vehicle interior and a deposited position opening up the vehicle interior. The folding top is deposited in a storage space behind the occupant compartment. In order to ensure that, in the closed position, the folding top covering material is under tension and rests on the folding top linkage, a material holding bow is provided in the rearward area of the vehicle roof and rests in the closed position of the folding top on the folding top compartment lid covering the storage space.
The known material holding bow is connected with the folding top covering material and acts upon the covering material by way of a tension which tightens the material. In order to prevent, as a reaction to the tensioning of the material, in the closed position, the material holding bow lifting off the folding top compartment lid, the material holding bow is held by a locking device on the vehicle body in its position in which it rests on the folding top compartment lid. The locking device consists of a snap lock which, in the closed position of the folding top, causes a locking of the material holding bow with the folding top compartment lid. In order to be able to erect the material holding bow during the transition movement of the folding top from the closed into the deposited position and to be able to open the folding top compartment lid, the snap lock can be unlocked by an electric-motor-driven actuator.
Although such locking devices between the material holding bow and a vehicle-body-side component are characterized by a high transmission of force and correspondingly a secure locking between the bow and the vehicle body, providing the possibility of subjecting the folding top to a high tension in the closed position, the locking device comprises a plurality of components which must be remote-controlled. The functions of the locking device as well as of the adjusting kinematics of the vehicle folding top must therefore be coordinated. Another problem is the fact that, particularly in the deposited position of the folding top, the vehicle-side locking devices become visible and may impair the overall appearance of the vehicle.
The type-forming DE 297 12 706 U1 describes a folding top whose folding top covering material is held under tension by a material holding bow in the closed position of the folding top. The material holding bow is acted upon by a tensioning hoop into which an articulated arrangement is placed which takes up an over-dead-center position in the closed position of the folding top.
Although the over-dead-center position provides a stable position of the tensioning hoop in the closed position of the vehicle roof, the stable position can be maintained only as long as no unacceptably high disturbance forces act upon the articulated arrangement in the tensioning hoop, which may be caused, for example, by the air stream at higher speeds and may be amplified particularly by a wear-caused play in the articulated arrangement. Thus, in the case of this arrangement, there is the risk that the tensioning hoop may accidentally buckle in its articulated arrangement.